Varicella zoster virus infection

Varicella zoster virus infection

Varicella zoster virus infection

During the primary infection there is a viraemic phasewhen VZV becomes widely disseminated in white cells. Innormal subjects it only produces significant lesions in theskin and mucous membranes, but infection of cutaneoussensory nerves leads to infection of dorsal root ganglia, andhere the virus enters a latent state. Reactivation latercauses herpes zoster (shingles). During primary infectionVZV is present in nasopharyngeal secretions and is transmittedreadily by coughing and sneezing. It is also in vesiclefluid in chickenpox and shingles, and this can be a sourceof transmission.The incubation period of chickenpox is 15-18 days andthe patient is infectious from a few days before the rasherupts until new lesions cease to appear.The severity of chickenpox is determined by the age andimmunological state of the patient. It is most severe inneonates if they have no maternal antibody to VZV, andin patients immunocompromised by disease such asleukaemia or by immunosuppressive therapy. It is usuallya mild disease in children, but it becomes increasinglysevere after puberty.

Clinical features In children chickenpox starts with the appearance of theMorphology Virus and diseaseEnveloped single-strandedNon-enveloped double-strandedNon-enveloped single-strandedOrthomyxoviridaeInfluenzaParamyxoviridaeParainfluenzaRespiratory syncytial diseaseMumpsMeaslesTogaviridaeRubellaAlpha (equine encephalitis)FlaviviridaeDengueYellow feverEncephalitisHepatitis CBunyaviridaeArenaviridaeLymphocytic choriomeningitisLassaFiloviridaeMarburgEbolaRetmviridaeLentiviruses (HIV 1 and 2)Oncoviruses - type C (HTLV1 and 2)RhabdoviridaeRabiesVesiculostomatitisCoronaviridaeCoronavirusReoviridaeRotavirusReovirusPicornaviridaeRhinovirusEnterovirusesCoxsackie A, BEchoPolioEnterovirus 70, 71Hepatitis ACaliciviridaeNorwalkHepatitis E virusAstroviridaeAstrovirusesrash, which is often sparse and not accompanied by constitutionalsymptoms. The most troublesome feature of theillness is itching. In adults there is a notable prodromalillness lasting 2-3 days, during which headache, backache,shivering and fever occur, sometimes with a sore throat andcough. The more severe the prodromal illness, the moreprofuse is the rash that follows.The rash starts on the trunk and spreads to the face andlimbs . Lesions appear in crops which progressrapidly through the sequence macule, papule, vesicle,pustule, scab. Often the first visible lesions are vesicles containingclear fluid with little surrounding erythema, but thepustular stage is reached within 24 hours. Vesicles on thepalate, tonsils and pharynx rapidly burst, leaving superficialulcers. Crops of skin lesions erupt over 2 or 3 days, butit takes several more days for them all to heal. Constitutionalsymptoms, if present, lessen with the onset of therash and disappear within 2 days.ComplicationsSecondary infection of the skin lesions, including the scalp,occurs because of scratching, but it usually responds tocleaning and bathing and rarely requires antibiotics.Chickenpox pneumonia occurs in one-fifth of adults,and more frequently in immunocompromised patients. Itvaries in severity from transient dyspnoea to a fulminantpneumonia.Postinfectious encephalitis is extremely rare and has avariable course, but it is often severe or fatal. Its onset iswithin a week of the rash and cerebellar involvement ischaracteristic.Bleeding into the skin, nose or intestine, also rare, is dueeither to steroid-responsive thrombocytopenia or to consumptivecoagulopathy, when the prognosis is much worse.Neonatal chickenpox

Most women are immune by the time they reach childbearingage, but if a mother develops chickenpox within afew days of having a baby the child is born without the protectionof maternal IgG antibodies transferred across theplacenta, and it is immediately exposed to the virus. If thechild becomes infected during the first 5 days of life diseaseis severe, with multi-organ involvement.Disease can be prevented or made milder by the administrationof varicella immune globulin 250 mgi.m. at birth.Aciclovir l0mg/kg is given intravenously 8-hourly for 7days if any signs of infection (e.g. fever) appear. This doesnot seem to prevent the virus becoming latent.Congenital chickenpoxRarely, VZV can cross the placenta during the first 20weeks of pregnancy, causing fetal damage or death.Diagnosis and managementA clinical diagnosis of chickenpox suffices in most cases.Electron microscopy is the quickest way to establish thata herpes virus is present in vesicle fluid, but does not establishits type. The virus can be identified by tissue cultureinoculation, and antibodies are detected by a complementfixation test.

Treatment with aciclovir is required only insevere cases susceptible to complications such as chickenpoxpneumonia, in immunocompromised patients (such aschildren with malignant disease), and in neonates. Intravenous treatment (l0mg/kgt.d.s in adults;500mg/m2 for children aged 3 months to 12 years; l0mg/kgfor children less than 3 months) is needed in order toachieve adequate serum concentrations. Many patientswith chickenpox pneumonia need ventilation and antibiotic treatment for secondary bacterial infection,the most common organism being Staphylococcus aureus.

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